This invention relates to constant pressure pumps and more particularly to a pump which will drive a fluid load with a constant pressure over a wide range of restrictions of the fluid load.
Precision pumps find many applications in industry and the laboratory. Metering pumps are used to deliver precise quantities of fluid. Examples of such metering pumps are shown in U.S. Pat. Nos. 3,149,469 and 3,335,670, W. A. Williams.
Metering pumps of the type shown in U.S. Pat. Nos. 2,263,429 and 2,367,893, Sheen and in U.S. Pat. No. 2,260,734, Saalfrank include a piston moving in a cylinder with inlet and outlet ports. The piston transfers precise quantities of liquid between the inlet and outlet ports as the piston reciprocates. Typically, the piston stroke is controlled by a motor driven micrometer drive.
Providing a pump which maintains a constant pressure is difficult because changes in the hydraulic load change the error and stability of the controller for the pump. It is difficult to neutralize the effect of the user's hydraulic system and provide constant performance with all fluid loads.